Indepth Electrical engineering

Miniature Circuit Breakers (MCBs) – Working & Internal Parts What is an MCB? An MCB (Miniature Circuit Breaker) is an electromechanical device that protects an electrical circuit from over-current. The over-current in a circuit may occur due to: Short circuit Overload Faulty design Unlike fuses, MCBs do not need replacement after tripping. Instead, they can be reset manually, offering better safety, convenience, and cost-effectiveness . MCBs are widely used in domestic and industrial applications , particularly for lighting loads and small motor loads . Working Principle of MCB The working of an MCB is straightforward: An MCB acts like a switch that turns off automatically when the current exceeds the permissible limit. It is designed to protect against over-current and over-temperature faults . How it works: There are two contacts: fixed and movable . When the current exceeds the set value, the solenoid pushes the movable contact to open ...

Vacuum Circuit Breaker (VCB): Working Principle, Operation, and Maintenance Guide A Vacuum Circuit Breaker (VCB) is one of the most reliable and widely used switchgear technologies for medium-voltage applications. It extinguishes arc inside a vacuum , where no medium (oil, gas, or air) is required, making it safer and more eco-friendly compared to conventional circuit breakers. Working Principle of VCB The main function of any circuit breaker is to quench the arc that forms when contacts open under load. In a VCB: The arc quenching medium is vacuum , with pressure maintained around 10⁻⁶ bar . When contacts separate, a metal vapor arc is formed at the last contact point. At current zero, the arc is extinguished as the vapor condenses back on the contacts. The high dielectric strength of vacuum (8× air, 4× SF₆) prevents re-ignition. This ensures fast arc extinction and minimizes contact erosion. Construction of Vacuum Interrupter A typical vacuum interrupter c...

Percentage Impedance of a Transformer (Z%) The percentage impedance (Z%) of a transformer is one of the most important parameters marked on its nameplate. It influences voltage regulation, fault levels, and load sharing when transformers are connected in parallel. Definition The percentage impedance of a transformer is: The voltage drop at full load caused by the resistance and leakage reactance of the windings, expressed as a percentage of the rated voltage. Alternatively, it can be defined as the percentage of rated terminal voltage required to circulate full-load current under short-circuit conditions. Measurement of Transformer Impedance Transformer impedance is measured by performing a short-circuit test : One winding of the transformer is short-circuited. A reduced voltage (at rated frequency) is applied to the other winding. The voltage is gradually increased until the rated full-load current flows through the windings. The percentage impedance ...

Strain Insulator Strain insulators working principle is same as that of suspension insulators and they have only difference is that when insulator used in vertical position then it is known as suspension insulator and when used in horizontal position then it is known as strain insulator.  When there is a dead end or there is a sharp corner in transmission line, the line has to sustain a great tensile load of conductor or strain. A   strain insulator   must have considerable mechanical strength as well as the necessary electrical insulating properties. Rated System Voltage Number of disc insulator used in strain type tension insulator string Number of disc insulator used in suspension insulator string 33KV 3 3 66KV 5 4 132KV 9 8 220KV 15 14 Stay Insulator   For low   voltage   lines, the stays are t...

Air Circuit Breaker (ACB): Working Principle, Operation, Advantages & Disadvantages Air Circuit Breakers (ACB) are among the most widely used types of circuit breakers, particularly in low-voltage (LV) and medium-voltage (MV) systems . As the name suggests, these breakers operate in atmospheric air pressure and use air as the arc-extinguishing medium. Traditionally, ACBs were also deployed in medium-voltage networks up to 15 kV , but with advancements in vacuum and SF₆ circuit breakers , their use in MV systems has declined. However, for low-voltage high-current applications (above 800A) , ACBs still remain a preferred and reliable choice . Working Principle of Air Circuit Breaker The primary objective of any circuit breaker is to interrupt current safely and prevent the arc from restriking once the current reaches zero. This is achieved by creating conditions such that the contact gap can withstand the system recovery voltage . In simple terms, arc quenching i...

Suspension Insulator As discussed earlier Pin type insulators are useful for using at 33KV and above 33 KV it becomes uneconomical to use Pin type insulators. This is mainly due to increased size, Weight of pin type insulator. Thus it become very difficult for handling and replacement of Such insulators. Due to above stated problem Suspension type insulators are developed. It is quite interesting to know about suspension insulators, Suspension type insulators consists of   numbers of insulators are connected in series to form a string and the line conductor is carried by the bottom most insulator. Each insulator of a suspension string is called disc insulator because of their disc like shape. Suspension type insulators are very economical to use and advantages and disadvantages for the suspension type insulators are as below:- Suspension Insulator Advantages:- 1. In suspension type insulators each disc is designed for normal   voltage ...

SF6 Circuit Breaker – Working, Properties, Advantages, and Disadvantages Introduction A circuit breaker that uses Sulphur Hexafluoride (SF6) gas as the arc-quenching and insulating medium is known as an SF6 Circuit Breaker . Due to its excellent dielectric and arc-extinguishing properties, it is one of the most widely used high-voltage (HV) and extra-high-voltage (EHV) circuit breakers, commonly employed in the range of 33 kV up to 800 kV and above . SF6 possesses unique electrical and thermal characteristics that make it nearly 100 times more effective than air as an arc-quenching medium. This has made SF6 circuit breakers a critical element in modern power transmission and distribution networks. Why SF6 Gas is Used in Circuit Breakers 1. High Electron Affinity SF6 is a highly electronegative gas , meaning it has a strong tendency to capture free electrons. When a free electron collides with an SF6 molecule, it is absorbed, forming a heavy negative ion: SF6 + e⁻ → SF6⁻ ...